This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. There is a readily recognizable PNPase-like molecule in human genome, which localizes to mitochondria and its deficiency leads to mitochondrial dysfunction. Importantly, we have found that a direct interaction between recombinant SUV3 and PNPase in vitro. We plan to further examine their interaction in detail to test whether SUV3 works in concert with PNPase in monitoring mitochondrial RNA degradation. Are there other proteins in degradosome together with SUV3/PNPase? If yes, what are their roles in RNA degradation? To isolate and identify the SUV3/PNPase complex from mitochondria are critical steps in advancing the current knowledge on mammalian mitochondrial degradosome. The crystal structure of influenza A virus NP has recently been determined in Tao's laboratory. Organized as trimers in the crystal, NP folds into a two-domain structure with a topology completely different from that of the rhabdovirus NP. A short tail loop, consisting of residues 402 to 428, is likely to play an important role in NP oligomerization, as single-residue mutation in this region causes a total loss of oligomerization. A large positively charged groove was identified at the exterior of the NP trimer at the interface between the two domains. An external RNA binding site indicates that RNA is likely to be exposed in the influenza virus RNPs, different from the situation in non-segmented RNA viruses [2]. To provide a definite evidence for our external RNA binding model and to elucidate RNP structure and assembly, we propose to determine the structure of the NP:RNA complex.